1. Technical Field
The present invention relates to a package for an electronic component including an interior space in which the electronic component is airtightly sealed, a piezoelectric device airtightly sealing a piezoelectric resonator element serving as the electronic component, and a manufacturing method of the piezoelectric device.
2. Related Art
Piezoelectric devices, such as crystal resonators, have been used in various information and communication devices, office automation (OA) equipment, and electronic apparatuses, such as consumer-electronics devices. Especially in recent years, significant progress in improving performance as well as downsizing and thinning of the electronic apparatuses and the like has been made. In order to respond to demands for smaller and thinner devices, surface-mounted piezoelectric devices suitably mounted on circuit boards have been widely used. In general, surface-mounted piezoelectric devices have a structure in which a piezoelectric resonator element is bonded in a package made of an insulating material, such as ceramic, and a lid is bonded on the package so as to seal the piezoelectric resonator element in a cavity formed by the package and the lid. However, the related-art package structure, in which a package and a lid are bonded with low-melting point glass or by seam welding, may lower or deteriorate frequency characteristics of piezoelectric resonator elements due to outer gas, high heat or the like generated in the seam welding.
For solving such problems, a piezoelectric device is proposed that includes a package composed of a first substrate and a second substrate and houses a piezoelectric resonator element serving as an electronic component in an interior space between two substrates. JP-A-2000-269775 is a first example of related art introducing a quartz resonator element serving as the piezoelectric device. In the first example, a resonator element substrate (quartz crystal element) in which a crystal resonator element integrally formed with a frame is provided between a first substrate (base substrate) and a second substrate (lid substrate) made of quartz crystal, glass or the like, and they are bonded to each other by direct bonding (surface activated bonding) so as to house the crystal resonator element in an interior space between the first substrate and the second substrate. The surface activated bonding is a bonding method in which bonding regions that are a corresponding surface for bonding of quartz crystal or glass mainly composed of silicon (Si) are mirror polished, brought into contact, and pressurized so as to directly bond the bonding materials by silicon bonds (interatomic bonds) of the contact surface. The bonding materials can be bonded substantially without heating.
JP-A-2004-254238 is a second example of related art introducing a method for manufacturing a piezoelectric device by using anodic bonding, which is a directly bonding method different from the surface activated bonding. In the second example, the piezoelectric device is manufactured as follows. A lid substrate and a base substrate are directly bonded with the resonator element substrate, in which a piezoelectric resonator element is formed, interposed therebetween. In a vacuum chamber, a sphere sealant made of metal or the like that fuses is provided in a sealing hole (through hole) formed in either one of the lid substrate and the base substrate. The sealant is melted and solidified so as to fill the sealing hole. Accordingly, the piezoelectric resonator element is airtightly sealed in an interior space formed by the lid substrate and the base substrate.
JP-A-2007-180924 is a third example of related art. In the piezoelectric device shown in the third example, however, the interior wall of the sealing hole has a linear shape toward a direction of penetration of the sealing hole. Therefore, when the sphere sealant is provided in the sealing hole, the portion contacting the interior wall of the sealing hole with the sealant is very small. When the sealant is melted for sealing the sealing hole, heat is not efficiently conducted to the sealant. Therefore, it is hard to promote melting of the sealant, and also the melted sealant is hard to wet and cover the interior surface of the sealing hole. Accordingly, it is hard to ensure airtight properties of the sealing, and reliability of the piezoelectric device may be decreased by malfunction of the piezoelectric resonator element due to sealing defects and influence of external factors.